(1) Field of the Invention
The present invention relates to a substrate treating apparatus and a substrate treating method for removing a liquid adhering on a substrate that may be of various type (hereinafter referred to merely as a “substrate”) from the substrate, examples of the substrate including a semiconductor substrate, a glass substrate for a photomask, a glass substrate for a liquid crystal display, a glass substrate for a plasma display, a substrate for an FED (field emission display), a substrate for an optical disc, a substrate for a magnetic disc, or a substrate for a magnetooptical disc.
(2) Description of Related Art
In a process for producing an electronic member such as a semiconductor device or a liquid crystal display device, a substrate is subjected to various wet treatments each using a liquid, and subsequently the substrate is subjected to a drying treatment for removing the liquids adhering on the substrate by the wet treatments.
One of the wet treatments is, for example, a washing treatment for removing pollutants on the surface of the substrate. For example, on a surface of a substrate in which a fine pattern having convexo-concavities is formed through a dry etching step, reaction byproducts (etching remnants) are present. Moreover, besides the etching remnants, metal impurities, organic pollutants and others may adhere on the substrate surface. In order to remove these substances, the washing treatment is conducted, in which a washing liquid is supplied to the substrate.
After the washing treatment, the substrate is subjected to a rinsing treatment for removing the washing liquid with a rinsing liquid, and a drying treatment for drying the substrate to dry the rinsing liquid. An example of the ringing treatment is rinsing treatment of supplying a rinsing liquid such as DIW (deionized water) to the substrate surface onto which the washing liquid adheres to remove the washing liquid on the substrate surface. Thereafter, the substrate is subjected to the drying treatment, in which the rinsing liquid is removed to dry the substrate.
In recent years, a pattern formed on a substrate has been made finer. With this tendency, convexities of a pattern, which has convexo-concavities, have been becoming larger in aspect ratio (ratio between the height and width of each of the pattern convexities). Consequently, when the substrate is subjected to a drying treatment, there arises a problem of the so-called pattern collapse. Specifically, surface tension acts to a boundary interface between a washing liquid, a rinsing liquid or any other liquid that enters the concavities of the pattern and a gas contacting the liquid; and by the surface tension, adjacent two of the convexities in the pattern attract each other to be collapsed.
As a drying technique for preventing such a pattern collapse, for example, JP 2013-16699 A described blow discloses a method of bringing a solution into contact with a substrate having a formed structure (pattern), converting the solution to a solid to form a support for the pattern, and changing the support from the solid phase to a gas phase, without causing the support to undergo any liquid phase, to remove the support. The patent document also discloses that a material for the support may be at least one of methacrylic-based resin materials, styrene-based resin materials and fluorinated carbon-based materials.
JP 2012-243869 A and JP 2013-258272 A each disclose a drying technique of supplying a solution of a sublimable substance on a substrate, evaporating any solvent in the solution to fill the upper of the substrate with the resultant solid sublimable substance, and then sublimating the sublimable substance. These patent documents state that no surface tension acts to the boundary surface between the solid and a gas contacting the solid so that pattern collapse caused by such a surface tension can be restrained.
JP 2015-142069 A discloses a drying technique of supplying a melted liquid of tert-butanol (t-butanol) to a substrate onto which a liquid adheres, solidifying t-butanol on the substrate to produce a solidified body, and then sublimating t-butanol to be removed.
However, the drying technique disclosed in JP 2013-16699 A has a problem that about substrates having a pattern fine and high in aspect ratio (in other words, a pattern in which the height of its convex pattern is larger than the width of the convex pattern), pattern collapse cannot be sufficiently prevented.
The drying technique disclosed in JP 2012-243869 A and JP 2013-258272 A need to supply a solution in which a sublimable substance is dissolved in a solvent to a substrate, and subsequently remove the solvent selectively on the substrate to precipitate the sublimable substance on the substrate.
For example, JP 2013-258272 A makes use of 1,2,3-benzotriazole as a sublimable substance. This patent document states that the melting point of this substance is 95° C., and a solution in which 1 g of 1,2,3-benzotriazole is dissolved in 20 mL of IPA (isopropyl alcohol) is supplied to a substrate and this substrate is heated at 50° C. or lower to vaporize IPA to precipitate the sublimable substance on the surface of the substrate. If at this time the sublimable substance is not precipitated in the state of being filled into concavities of a pattern of the substrate, there remains a problem that surface tension acts ultimately to the substrate pattern to make it impossible to prevent the collapse of the pattern. This problem becomes more remarkable as the pattern is made finer.
In the drying technique disclosed in JP 2015-142069 A, a melted liquid of t-butanol is supplied to a substrate and then t-butanol is solidified, so that this technique does not use the precipitation of a sublimable substance by solvent-removal, which is performed in JP 2012-243869 and JP 2013-258272. Thus, this technique can cope with the above-mentioned problems. However, even the use of the sublimating and drying technique using t-butanol may not make it possible to prevent the collapse of a pattern fine and high in aspect ratio sufficiently.
Furthermore, each of the above-mentioned patent documents does not solve a problem that pattern collapse generated by a cause other than the effect of surface tension to a pattern cannot be sufficiently restrained. For example, when organic substances are present as impurities in a solution containing a sublimable substance, the organic substances may turn to crystal nuclei when this sublimating-substance-containing solution is solidified. In this way, each of the impurities has turned to the crystal nuclei so that crystal grains grow. The grown crystal grains soon collide with each other to generate crystal grain boundaries at boundaries between the grains. The generation of the crystal grain boundaries causes stress to be applied to the pattern to cause a problem that pattern collapse is generated.